POSIX strerror_r returns an error number, not -1

The posix spec says strerror_r returns a positive error number,  not
-1 and set errno.

Test: bionic-unit-tests-static
Change-Id: I6a12d50d046f9caac299bf3bff63e6c9496c1b6f

2 files changed, 5 insertions, 6 deletions

diff --git a/libc/bionic/strerror.cpp b/libc/bionic/strerror.cpp
index 57335674b..0deb2000f 100644
--- a/libc/bionic/strerror.cpp
+++ b/libc/bionic/strerror.cpp
@@ -196,8 +196,7 @@ int strerror_r(int error_number, char* buf, size_t buf_len) {
     length = async_safe_format_buffer(buf, buf_len, "Unknown error %d", error_number);
   }
   if (length >= buf_len) {
-    errno_restorer.override(ERANGE);
-    return -1;
+    return ERANGE;
   }
 
   return 0;
diff --git a/tests/string_posix_strerror_r_test.cpp b/tests/string_posix_strerror_r_test.cpp
index 596684b56..67b3c1f90 100644
--- a/tests/string_posix_strerror_r_test.cpp
+++ b/tests/string_posix_strerror_r_test.cpp
@@ -55,10 +55,10 @@ TEST(string, posix_strerror_r) {
   // Buffer too small.
   errno = 0;
   memset(buf, 0, sizeof(buf));
-  ASSERT_EQ(-1, strerror_r(4567, buf, 2));
-  ASSERT_STREQ("U", buf);
-  // The POSIX strerror_r sets errno to ERANGE (the GNU one doesn't).
-  ASSERT_EQ(ERANGE, errno);
+  ASSERT_EQ(ERANGE, strerror_r(EPERM, buf, 2));
+  ASSERT_STREQ("O", buf);
+  // POSIX strerror_r returns an error without updating errno.
+  ASSERT_EQ(0, errno);
 }
 
 #endif